Change anchor to button element (#3321)

Fix warning for ESLint (jsx-a11y/href-no-hash).

app/javascript/mastodon/components/load_more.js

@@ -3,9 +3,9 @@ import { FormattedMessage } from 'react-intl';
 import PropTypes from 'prop-types';
 
 const LoadMore = ({ onClick }) => (
-  <a href="#" className='load-more' role='button' onClick={onClick}>
+  <button className='load-more' onClick={onClick}>
     <FormattedMessage id='status.load_more' defaultMessage='Load more' />
-  </a>
+  </button>
 );
 
 LoadMore.propTypes = {